Graphene is a single-layer crystal arranged in a two-dimensional honeycomb lattice by carbon atoms in SP2 hybridization. The graphene is not limited to a graphite in a single-layer structure of carbon atoms, but can be a graphite comprising two or more layers of carbon atoms, as long as it behaviors like a two-dimensional crystal.
Studies on semiconductor devices using graphene have been conducted recently. A graphene nano-ribbon has a nanoscale width. Due to a size effect, the graphene nano-ribbon has a limited band gap and behaviors like a semiconductor.
U.S. patent application No. US2010/0102292A1, by Hidefumi Hiura, et al., discloses a semiconductor device using graphenes, in which a graphene semiconductor is suitably doped to provide a channel region, and a graphene metal is used to provided source/drain regions and a gate.
However, the above semiconductor device uses only a single graphene nano-ribbon to form the channel region, and carries only a small amount of on-state current.
Moreover, the known methods for manufacturing the graphene nano-ribbon include either the steps of forming a graphene layer by pyrolyzation and patterning the graphene layer, or the steps of stripping a thin graphene layer from a thick graphene layer and transferring the thin layer, to form a graphene layer having both a nanoscale thickness and a nanoscale width. The known methods for manufacturing the graphene nano-ribbon are expensive in cost and may result in fluctuation in processes, because it is difficult to control sizes of the grapheme nano-ribbon in both dimensions.